Process for stabilizing organic heavy metal salts



Patented May 7, 1940 PATENT OFFICE PROCESS FOR STABILIZING ORGANIC HEAVYMETAL SALTS Mihai Bogdan, Ploesti, Rumania, assignor to ShellDevelopment Company, San Francisco, Calif., a corporation of Delaware 7No Drawing, Application May}, 1938, Serial No. 205,757. In theNetherlands May 13, 1937 Claims.

This invention relates to the stabilization of heavy metal salts ofrelatively high molecular weight non-aromatic monocarboxylic acids whichhave a tendency to decolorize upon storage or 5 exposure to air, andmore particularly is concerned with inhibiting discoloration of organicheavy metal salts used for driers in paints, by the addition of smallamounts of certain antioxidants.

Salts of heavy metals and non-aromatic relatively high molecular weightmonocarboxylic acids,'i. e. having 7 or more carbon atoms, such asnaphthenic acids, abietic acid, fatty acids of 7 or more carbon atoms,acids obtained in' the oxidation of paraffin wax or other relativelyhigh molecular weight non-aromatic hydrocarbons, e. g. polymers ofolefines, have a variety of important uses. Thus salts of cobalt, iron,manganese, and lead are used as paint driers; copper and mercury areused as parts of insecticides and wood-preserving agents, others may beused in lubricating oils to increase the load-carrying capacity of oilfilms or to prevent piston ring sticking in internal combustion engines,etc. These salts may be prepared directly from the free acids or bydouble decomposition of their alkali metal salts. When freshly preparedfrom reactants having reasonable degrees of purity, the salts usuallypossess clear colors.

30 It has been found that many of the above heavy metal salts, bythemselves or in solutions of suitable solvents, have a tendency tobecome discolored more or less rapidly upon storage in open or closedcontainers and more particularly when spread out as thin films on solidsurfaces. The colors turn muddy dark and may even become black. Suchchanges in the colors are obviously highly undesirable and harmful,especially in the case of paint driers. For instance, a White paintcontaining lead naphthenate drier 40 has been known to turn an unsightlygray because of the discoloration of the drier and thus becomealtogether unusable.

The discoloration is usually most noticeable in the case of heavy metalnaphthenates, particularly those prepared with naphthenic acidsoriginating from relatively heavy mineral oils, i. e. gas oil fractionsand heavier. For example. a cobalt naphthena'tewhich when fresh had a 50clear blue color turned brown within 12 hours when exposed to theatmosphere. Darkening is often accompanied by loss of other important.

properties such as solubility in many of their common solvents, abilityto promote drying, etc. I have discovered that this discoloration cantical purposes.

be inhibited or at least be greatly retarded by finely distributingcertain anti-oxidants throughout the salts hereinbefore described.Although the underlying reactions which are,responsible for thediscoloration have not been explained, it 5 is believedthat they are insome way connected with oxidation.

Particularly susceptible to the inhibiting action of the anti-oxidantsdescribed later are'the naphthenates derived from petroleum naphthenicacids and abietates; and as to the various heavy metals the cobalt saltsusually seem to respond most readily to the inhibitors.

Of the large class of substances known to be active anti-oxidants,p-phenylene diamine, 0- phenylene diamine, p-amino-phenol, o-aminophenol, 1-2, l-4, 1-5, l-7 and 1-8 naphthylene diamines and aminonaphthols, diphenyl thio urea, and alkyl and aralkyl derivatives thereofhave been found to give the most effective pro- 20 tection against"discolorations. Certain other well-known anti-oxidants as cetyl aniline,phenol, hydroquinone, pyrogallol, ethylene trithio carbonate, diphenylamine, m-phenylene diamine, m-ammo naphthol, l-3 amino naphthol, and a25 host of others have very little color-inhibiting power for the saltsherein described, and some anti-oxidants such as the m-amino phenol, 1-3amino naphthol, cetyl aniline, pyrogallol etc., may even be definitelyharmful, in that they accelerate rather than inhibit discoloration.Again other anti-oxidants such as beta naphthol, beta naphthyl amine,etc., have some inhibiting power, which. however, is insuflicient formost prac- Mixtures of active anti-oxidants are often more efiectivethan their individual components. Thus a mixture of 80% methylatedp-amino phenol and 20% methylated p-phenylene diamine was one. of themost effective inhibitors encountered. In some instances wood tarfractions boiling above 240 C. have given good results.

The quantities of the anti-oxidants required for efiective stabilizationof the metal salts are normally below 2% and usually between about to 1%by weight of the organic acid in the sa The anti-oxidants may beincorporated into the salt by dissolving the latter in a suitable 5osolvent and dissolving the inhibitor in the same solvent before, afteror simultaneously with the salts; or a separate solution of theinhibitor. may be added to the salt solution; or the inhibitor may bedissolved in the carboxylic acid prior to preparing the salt in caseswhere this does not interfere with the preparation of the salt. If asolvent was used for incorporating the antioxidant, after removal of thesolvent by evaporation, distillation, etc., the anti-oxidant remainsextremely finely distributed throughout the salt, though perhaps not intrue solution.

In the following illustrative examples, the efiect of the inhibitor onthe color was measured by comparing the colors at different timeintervals of several samples of a salt of the type described, with andwithout inhibitor, spread as thin films on carefully cleaned glassplates, after exposure to air.

Example I Cobalt naphthenate was prepared by neutralizing gas oilnaphthenic acids with an aqueous solution of caustic soda. The resultingsolution was shaken with benzene and an equivalent amount of cobaltchloride dissolved in water.

The mixture was then allowed to stand and separate. The benzene layer,which contained the cobalt naphthenate, was removed and was furtherdiluted with benzene so that it contained exactly 2.75 gm. naphthenicacid per 10 ml solution.

To samples of the resulting solutions various inhibitors in an amount of1% by weight of the naphthenic acid (or less as explained below) wereadded, If necessary, the solutions were warmed to effect completedissolution of the inhibitors. In some instances where the inhibitorscould'not be readily dissolved they were first dissolved in ethylalcohol and the resulting solutions were added to the naphthenatesolution.

6 to '7 drops of the several naphthenate solutions were then placed onglass plates and allowed to spread and dry. The plates were then exposedto air at 50 C. for several'days. The colors were noted at intervals ofone day. Results were as follows:

Color after number of d y Inhibitor Blank p-Amino phenol Benzylamino-p-phenol -Phenylene diamine- -amino 5-naphthoL. l-amino 7-naphthol 1-5 naphthylene diamine. 1-8 naphthylene diamine Diphenyl thio ureaBeta naphthol Wood tar Dlphenyl emine Hydroqumone dowwwmwmwwmmee awmwwmwwwwmw evnwmmmmwmm e mmwwnmmw wvmwmmwm l-amino 3-naphthoL.

Ethyl tolyl sulfide Ethylene trithlo carbonate- Cetyl-anihneou'mommmmwmmmmwwwwwmwm contains less than 1% inhibitor because ofincomplete solubility. contains 0.1% inhibitor.

" conta ns 0.05% inhibitor.

b=imtia slight discoloration.

c=dlscolored.

Example II Cobalt abietate'was tested by the method described for theprevious example. Without inhibitor the abietate was completelydiscolored after one day. /3% by weight of an inhibitor consisting of amixture of 80% methylated I o-phenylene diamine, p-phenylene 1 o-aminophenol, p-amino phenol, benzyl amino p-amino phenol and 20% methylatedp-phenylene diamine caused the color to remain clear for three days. Onthe fourth day discoloration began to appear. 1

Equal amounts of phenol and alkyl phenols had no inhibiting effects.

Example I II Cobalt linoleate which discolored in less than 24 hours bythe test method of Example I did not discolor for several days afteraddition of an inhibitor consisting of a mixture of 80% methylatedp-amino phenol and 20% methylated p-phenylene diamine in an amount of 1%by weight of the linoleic acid.

I claim'a's my invention: 1.'In a process for inhibiting discolorationof a salt of a heavy metal and an organic acid selected from the groupconsisting of aliphatic and alicyclic monocarboxylic acids containing atleast 7 carbon atoms, the step comprising finely distributingthroughout. said salt an anti-oxidant selected from the group consistingof o-phenylene diamine, p-phenylene diamine, o-amino phenol, p-aminophenol, benzyl aminop-phenol, 1-2 naphthylene diamine, 1-4 naphthylenediamine, 1-5 naphthylene diamine, 1-7 naphthylene diamine, l-8naphthylene diamine, 1-2

naphthol, in an amount of 0.02 to 2% by weight of said acid.

2. A salt of a heavy metal and an organic acid selected from the groupconsisting of aliphatic and alicyclic monocarboxylic acids having atleast 7 carbon atoms, said salt containing distributed an amount ofextremely finely divided antioxidant selected from the group consistingof diamine,

p-phenol, 1-2 naphthylene diamine, 1-4 naphthylene diamine, 1-5naphthylene diamine, 1-7 naphthylene diamine, l-8 naphthylene diamine,1-2 amino naphthol, 1-4 amino naphthol, 1-5 amino naphthol, 1-7 aminonaphthol, and l-8 amino naphthol, said amount being between 0.02 and 2%byweight of said acid.

3 3. A salt of a heavy metal and naphthenic acids obtained from amineral oil boiling not below gas oil, said salt containing distributedan amount of extremely finely divided anti-oxidant selected from thegroup consisting of o-phenylene diamine, p-phenylene diamine, o-aminophenol, p-amino phenol, benzyl amino p-phenol,

, l-2 naphthylene diamine, 1-4 naphthylene di amine, 1-5 naphthylenediamine, 1-7 naphthylene diamine, 1-8 naphthylene diamine, 1-2 aminonaphthol, 14 amino naphthol, 15 amino naphthol, 14 amino naphthol, and1-8 amino naphthol, said amount being between 0.02 and 2% by weight ofsaid naphthenicacids. p

4.. A salt of cobalt and an organic acid selected from the groupconsisting of aliphatic and allcyclic monocarboxylic acid having atleast '7 carbon atoms said salt containing distributed an amount ofextremely finely divided anti-oxidant selected from the group consistingof o-phenylene diamine, p-phenylene diamine, o-amino phenol, p-aminophenol benzyl amino p-phenol, 1-2 naphthylene diamine, 1-4 naphthylenediamine, 1-5 naphthylene diamine, l-'7 naphthylene diamine, 1-8naphthylene diamine, 1-2 amino naphthol, 1-4 amino naphthol, 1-5 aminonaphthol, 1-7 amino naphthol, and 1-8 amino naphthol, said amount beingbetween 0.02 and 2% by weight of said acid.

5. A cobalt naphthenate containing distributed an amount of extremelyfinely divided antioxidant selected from the group consisting ofo-phenylene diamine, p-phenylene diamine, o-amino phenol, p-aminophenol, benzyl amino p-phenol, 1-2 naphthylene diamine, 1-4 naphcobaltnaphthenate.

MIHAI BOGDAN.

